Method of casting cellulose sheets from solutions of cellulose



Dec. 27, 1932. c. H. VON HOESSLE 1,392,657

METHOD OF CASTING CELLULOSE SHEETS FROM SOLUTIONS OF CELLULOSE Filed Nov. 3. 1930 FIG. 1

iZMWWM INVENTOR gww ATTORNEY Patented Dec. 27, 1932 UNITED STATES PATENT OFFICE CARL HERMANN VON HOESSLE, OF RADEBEUL-DRESDEN, GERMANY, ASSIGNOR TO CHEMISCHE FABRIK VON HEYDEN, AKTIENGESELLSCHAFT, OF RADEBEUL, NEAR DRESDEN, GERMANY, A CORPORATION OF GERMANY METHOD OF CASTING OELLULOSE SHEETS FROM SOLUTIONS OF CELLULOSE Application filed November 3, 1930, Serial No. 493,023, and in Germany November 7, 1929.

This invention relates to long and transparent sheets of cellulose and it particularly relates to such sheets made of cellulose solutions or the solution of its esters, and ethers, the object of the invention being to provide means by which certain more or less mechanical difficulties in the formation of a long thin sheet, or web, of cellulose will be overcome.

According to my invention a viscose sheet of even thickness, without any thick streaks, elevations and other disturbing irregularities is produced.

Other features of the invention will appear as the specification proceeds and in order to have the invention properly understood, I am going to describe the same by way of example in connection with the operation of casting the sheet from the well known viscose solutions.

In the prior art the long webs of this transparent cellulose sheet, made of viscose, are usually produced by causing a viscose solution to flow upon a horizontally disposed rotating drum, or cylinder, which is with its lower part immersed into a solution capable of precipitating the viscose from its solution. For this purpose the viscose solution is contained in a trough-like receiver placed above the cylinder and flows over the surface of the latter; the thickness and the width of the wetfilm, formed on the cylinder, is limited by a slot, which the rear wall of the reservoir forms with its lower edge and the surface of the cylinder. The opening is usually of regulatable dimension. In other devices the viscose solution flows from a receiver, or trough, through an opening regulated by a suitable valve, upon the cylinder and the thickness of the sheet to be formed is regulated by a roll arranged in the rear of the hopper. The operation of such devices is rather diiiicult and leads even with the greatest precaution to unsatisfactory results. Efforts have been made to overcome these difiiculties by substituting the cylinder with its auxiliary parts by a wide funnel, or trough, provided at its lower part with a slot which is arranged so low that it immerses directly into the precipitating bath and the viscose enters immediately into the precipitating liquid. The side edges of this slot must be of excellent work manship as otherwise the fine viscose film is full of irregularities and streaks right from the beginning of its formation and it would go too far to point out here the far reaching influences played by dust, corrosion, and other more or less difiicultly controlled fac tors, the expansion of metals, warping of wood, etc., which all mayccntribute to the blemishes later on found in the finished cellulose sheets.

I have now found that I can obtain very smooth sheets of cellulose and highly resistant to tearing by arranging the viscose solution in a trough having at its lower side slots formed by the front and rear wall suitably joined at its sides. One of the walls forming this slot is cut short while the other extends for some distance so as to form an apron. The distance for which I extend the one wall or apron may be a few centimeters, or considerably more until it dips into the precipitating agent.

I prevent the viscose solution from entering immediately into the precipitating liquid and conduct it first outside over the extended apron which I allow to dip only slightly into the precipitating liquid. This viscose solution is thus given time to evenly spread over the apron; any eventual uneveness, caused by the slot, is smoothed out during the travel over this apron. This is an important improvement for I obtain in this manner a beautiful and even viscose sheet which is of course subsequently treated in certain other baths.

I have furthermore found out that it is advantageous to bend the viscose sheet, or web, immediately upon its gliding off the apron so as to then pass it along in a substantially horizontal direction through the pre cipitating bath. This step also contributes to rendering the surface of the viscose sheet considerably smoother and even.

In connection with the above described steps I have found it also advantageous to subject the web to a stretching action. The drawing of the web. around the sharp edge at the lower end of the apron in itself exerts a certain strain on the sheet. The combination Cit of bending and drawing which is very benei'icial to the exterior physical properties of the obtained product.

The web may be subjected to a further stretching action by drawing it along the precipitating baths by cylinders, the speed of which may be suitably regulated.

For the better understanding of my invention I am going to describe how I proceed in the operation of the same, reference being had to the accompanying drawing, in which Figure l a front elevation and partly a vertical section on the line A-A of Figure 2 of an apparatus which is only an example of the various devices applicable to carrying my invention into efiect.

Figure 2 is a vertical section of the appa ratus on the line BB of Figure 1 showing particularly the means to bend the sheet and to pass it in substantially horizontal direction through the bath.

In the drawing 1. denotes a basin filled with a liquid 2 containing an agent, for instance ammonium chloride, capable of precipitating viscose from its solution.

2:3 denotes a trough, of slightly greater length than the width of the viscose sheet to be made, the trough being arranged above the basin 1. This trough 3 may have any suitable form; it may for instance consist, as illustrateth of two walls 4 and 5, of which the latter extends downwardly into an apron 6 terminating within the liquid 2 slightly be low the level of the same. The trough 3 is provided with a slot 7' and the viscose solution 8. filling the trough 3, flows out of the same through the slot 7 down the apron 6 into the liquid 2, which coagulates it.

The viscose sheet 8 glides off the apron 6 on account of its weight and as soon as a few inches of the gelatinous sheet, or web, denoted by numeral 9, have become free of the apron, it is caught. bent around the apron 6 and conducted in a horizontal direction around a glass rod 10 ar 'anged horizontally within the liquid For the present description it is assumed that a thin web is desired which on account of its desired thinness does not need to stay so long in the liquid 2, and passed quicker through the same by means of the rotary cylinder 11 arranged at the rear above the basin 1. if a thicker viscose sheet is made, the coagulating agent is allowed to act for a longer time on the gelatinous web 9.

It may be made of any material inert to viscose. particularly it may be of glass, nickel or a steel resistant to chemical influences. I wish to say finally that the stretching action to which the web 9 is subjected may be regulated by varying the speed of the rotary cylinder 11. For this purpose cylinder 11 or other cylinders by which the web is drawn along the different precipitating or washing baths is provided with special motion imparting means.

The cellulose sheet obtained after being entirely solidified bleached and washed may be dried according to any method known in the art.

The invention is also applicable to all cellulose solutions for instance also to solutions of esters and others of cellulose. The precipitating liquid must of course be adapted to the nature of the respective cellulose derivative.

hat I claim is:

1. The method of casting a cellulose solution into a smooth thin sheet by interaction with a. precipitating agent that method comprising spreading the cellulose solution directly on a plane substantially vertically disposed surface into a smooth liquid sheet while out of contact with the aforesaid agent before gelatinizing the sheet.

2. The method of casting a cellulose solution into a smooth thin sheet by interaction with a precipitating agent that method com prising spreading the cellulose solution directly on a plane substantially vertically disposed surface into a smooth liquid sheet while out of contact with the aforesaid agent acting upon the sheet with aforesaid agent thereby gelatinizing the sheet.

3. The method of casting a cellulose solution into a smooth thin sheet by interaction with a precipitating agent that method comprising spreading the cellulose solution directly on a plane substantially vertically disposed surface into a smooth liquid sheet while out of contact with the aforesaid agent acting upon the sheet with aforesaid agent thereby gelatinizing the sheet and stretching it.

4. The method of casting a cellulose solution into a smooth thin sheet by interaction with a precipitating agent that method comprising spreading the cellulose solution on a plane surface into a smooth liquid sheet outside the aforesaid agent acting upon the sheet with aforesaid agent thereby gelatinizing the sheet and stretching it by drawing the sheet around the sharp edge at the lower end of the aforesaid plane surface.

5. The method of casting a cellulose solution into a smooth thin sheet by interaction with a precipitating agent that method comprising spreading the cellulose solution on a plane surface into a smooth liquid sheet outside the aforesaid agent acting upon the sheet with aforesaid agent thereby gelatinizing the sheet and stretching it by drawing the sheet around the sharp edge at the lower end of the aforesaid plane surface and moving it substantially horizontally through the precipitating agent.

In witness whereof I have hereunto set my hand.

CARL HERMANN voN HOESSLE. 

